The present disclosure relates to a servo pattern writing method of a hard disk drive (HDD) and an HDD manufactured by the same, and more particularly, to a servo pattern writing method of an HDD capable of writing a servo pattern written on a servo track of a disk, and an HDD manufactured by the same.
A hard disk drive (HDD) is a data storage device configured to recode a digital electronic pulse including data information on a disk by converting into a magnetic field, or configured to read data written on a disk. Such HDD is being utilized as a representative auxiliary memory device of a computer system, due to its advantage to record and read (reproduce) a large amount of data at a high speed.
In order to successfully perform read and write operations of such HDD, a precise position should be searched by reading a servo pattern written on a servo track of the disk.
In the conventional art, the servo pattern is written onto a disk assembled to the HDD by using a servo track writer. The method for writing a servo pattern on a disk using a servo track writer has a disadvantage that accuracy of writing is degraded due to Non-Repeatable Run Out (NRRO), disk flutter, motor vibration, etc. Furthermore, costs associated with servo writing are increased according to usages of a position estimator and an encoder.
In order to solve such problems, a self-servo write method and an offline servo track write (OLSTW) method have been developed.
According to the self-servo write method, a reference servo pattern is firstly written by a servo track writer, on one of disks assembled to each other. Then, the HDD records a final servo pattern on the disks, with reference to a reference servo pattern written on a reference disk by a servo track writer.
In the self-servo write method, the quality of a final servo pattern is determined according to accuracy of the reference servo pattern. Furthermore, the self-servo write method is advantageous in the aspect of cost, since dependency on the conventional servo track writer is small. However, the self-servo write method is disadvantageous in that time for self servo writing is increased.
According to the OLSTW method, a servo pattern is pre-written on disks by using an offline servo track writer before mounting the disks to the HDD. The OLSTW method is advantageous in that productivity is greatly enhanced since a servo pattern is written at a time on 10 or more disks by an offline servo track writer.
A final servo pattern can be directly written by an offline servo track writer. However, an offline servo copy method for copying a final servo pattern after writing a reference servo pattern and then assembling an HDD. In this case, the productivity can be more enhanced.
A method for writing a reference servo pattern includes a burst method and a spiral method. According to the burst method, a reference servo pattern is spirally written on a disk, and a final servo pattern is written with reference to the reference servo pattern. According to the spiral method, a spiral reference servo pattern of a spiral shape is written on each disk, and a final servo pattern is written with reference to the spiral reference pattern. It is known that the offline servo copy method using spiral reference servo patterns is the most productive.
However, the offline servo copy method has the following problems. Firstly, the offline servo copy method uses a bank copy method for assembling a blank disk with a reference disk on which a reference servo pattern has been written, and then simultaneously writing final servo patterns on the entire disk surface from the reference servo patterns. In this case, the quality of a pattern onto which servo copy is performed is lowered as the disk surface is farther from the reference servo patterns according to a mechanical characteristic of the assembled HDD.
An HDD may not perform bank servo copy due to such mechanical limitations. In this case, multi pass servo copy, not the bank copy should be applied.
According to the multi pass servo copy, the final servo patterns are not simultaneously written on the surface of the entire disks unlike the bank copy, but servo copy is performed by using the reference servo patterns of the disks. In this case, servo copy is performed a plurality of times in the aspect of the entire drive, which is the reason why the servo copy is called multi pass servo copy.
According to the multi pass servo copy, the final servo patterns are independently written on the disks by using the reference servo patterns written onto the surface of all the disks. Therefore, only when the reference servo patterns written on the disks are aligned with each other, the final servo patterns which are to undergo servo copy from the reference servo patterns are aligned.
However, the reference servo patterns of a plurality of reference disks formed by an offline servo track writer are not always aligned with each other. In this case, as shown in FIG. 1, final servo patterns 700 and 800 are not aligned with each other in a horizontal direction of the disk surface.
FIG. 1 is a view illustrating a reference servo pattern and a final servo pattern on the same plane, the patterns respectively written on two disks, during offline multi pass servo copy according to one embodiment of the conventional art. As shown in FIG. 1, if a reference servo pattern 500 of a disk 1 is not aligned with a reference servo pattern 600 of a disk 2, the final servo pattern 700 of the disk 1 and the final servo pattern 800 of the disk 2 servo-copied from the reference servo pattern 500 of the disk 1 and the reference servo pattern 600 of the disk 2, respectively are not aligned with each other in a horizontal direction of the disk surface.
Even if the final servo patterns are not aligned with each other, a mis-aligned amount can be measured to be compensated during head switching. However, such process is very difficult and performance of the head switching may be degraded. Therefore, in case of applying the multi pass servo copy, the OLSTW method cannot be used, but the conventional servo track writer should be used. This may lower the productivity.